Pulse width modulation with discharge to suction bypass

ABSTRACT

A pulse width modulation control is provided for a suction valve located on a suction line. When the flow rate through a refrigerant system needs to be reduced, the suction valve is rapidly cycled from an open position to a closed position. A bypass line connecting compressor discharge to compressor suction with a bypass valve and a discharge valve positioned on the discharge side of the compressor are also provided. When the control closes the suction valve, it also closes the discharge valve to prevent the refrigerant to backflow into the bypass line, and, at the same time, the control opens the bypass valve. Opening of the bypass valve reduces discharge pressure, leading to reduction in compressor power consumption and subsequent operating efficiency gain.

BACKGROUND OF THE INVENTION

This application relates to a control for a refrigerant system whereinpulse width modulation technique is utilized to improve refrigerantsystem control and wherein a discharge bypass is operated in conjunctionwith the pulse width modulation to reduce compressor power consumption.

Refrigerant systems are utilized in many applications to condition aclimate controlled environment. In particular, air conditioners and heatpumps are employed to cool and/or heat air entering the climatecontrolled environment. The cooling or heating load in the environmentmay vary with ambient conditions, occupancy level, and changes insensible and latent load demands, and as the temperature and/or humidityset points are adjusted by an occupant of the environment.

Various features are known for providing adjustments in refrigerantsystem capacity. One approach which has been utilized in the prior artfor reducing the capacity of a refrigerant system is the use of pulsewidth modulation technique to control a fast acting solenoid valve on acompressor suction line. By rapidly cycling this valve utilizing pulsewidth modulation techniques, additional and accurate capacity control isprovided.

The goal of the pulse width modulation control is to efficientlycompress the refrigerant at reduced mass flow rates. This is done whenthe thermal load demand on the refrigerant system is lower than would beprovided with a compressor that is fully loaded.

However, this technique does not always achieve the goal of desiredefficiency improvement, because even though the suction pressure isreduced substantially when the suction valve is closed (or almostclosed), the discharge pressure still remains high causing a compressorpower consumption to be higher than desired. Moreover, the compressedrefrigerant on the discharge side can backflow into the compressionchambers, further increasing compressor power consumption due to thisbackflow refrigerant re-compression. This problem is particularly acutein compressors that are not equipped with a dynamic discharge valve (asis often the case for compressors used in standard air conditioningapplications). The absence of the dynamic discharge valve causes thecompressed refrigerant at the discharge pressure to flow back into thecompressor compression pockets, promoting increased power consumption.However, the problem also exists in compressors with a dynamic dischargevalve, where the refrigerant still needs to be compressed to thedischarge pressure. Refrigeration type compressors would normally be anexample of compressors used with a dynamic discharge valve.

SUMMARY OF THE INVENTION

In the disclosed embodiment of this invention, a compressor isassociated with a refrigerant system. The refrigerant system has a valvecapable of rapid cycling. The valve is installed on a suction line, anda pulse width modulation control is provided for that suction valve. Thepulse width modulation control is operable to rapidly cycle the valvefrom an open position to a closed position to change the capacity of therefrigerant system by controlling the amount of refrigerant delivered tothe compressor.

A bypass line is provided to connect the compressor discharge side tothe suction side; this bypass line also includes a bypass valve. Whenthe suction valve is moved to a closed position by the pulse widthmodulation control, the bypass valve is opened. In this manner, thecompressed refrigerant is returned to the suction line of thecompressor. In a disclosed embodiment, the bypass line returns therefrigerant to a location downstream of the suction valve. Since thecompressor discharge is now directly connected to the suction line, therefrigerant is not compressed to as high a pressure, and compressorpower consumption is significantly reduced.

Although, for illustrative purposes, this invention is described inrelation to refrigerant systems incorporating scroll compressors, it isapplicable to other compressor types as well.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a refrigerant system incorporating thepresent invention.

FIG. 2 shows a pressure versus volume graph for the compressor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A refrigerant system 19 is illustrated in FIG. 1 having a scrollcompressor 21 incorporating a non-orbiting scroll member 22 and anorbiting scroll member 24. As is known, a shaft 26 is driven by anelectric motor 28 to cause the orbiting scroll member 24 to orbit. Anoil sump 32 and an oil passage 34 in the shaft 26 supply oil to variousmoving elements in the compressor 21, as known.

A condenser 36 is positioned downstream of the compressor 21, anexpansion device 38 is located downstream of the condenser 36, and anevaporator 40 is positioned downstream of the expansion device 38, asknown. As is also known, the compressor 21 is driven by the electricmotor 28 to compress a refrigerant and to drive it throughout therefrigerant system 19.

The control 30 may be a microprocessor or other type control that iscapable of providing pulse width modulation control to a suctionmodulation valve 210 positioned on a suction line 212. It should beunderstood that the control 30 includes a program that accepts inputsfrom various locations within the refrigerant system, and determineswhen the pulse width modulation of the suction modulation valve 210needs to be initiated. Controls capable of performing this inventionwith such suction modulation valves are known in the art. The valveitself may be a solenoid type valve, again as known.

Now, when the control 30 determines that it would be desirable to reducecapacity of the refrigerant system 19, the suction modulation valve 210is rapidly cycled from an open position to a closed position (with acycle rate typically in the 3 to 36 second range) using a pulse widthmodulation control. For the pulse width modulation cycle, a closedposition for the suction modulation valve 210 does not have to be afully closed position and an open position for the suction modulationvalve 210 does not have to be a fully open position.

As is known, the compressor housing shell is sealed such that, whencompressor is running, there is a suction pressure in a chamber 121, andthere is a discharge pressure in a chamber 123, after the refrigeranthas been compressed by the orbiting movements of one of the scrollmembers 22 and 24 in relation to the other.

As shown, a discharge valve 200 is positioned in a discharge tube 202(the valve can also be positioned in the discharge line 206, whichconnects the discharge tube 202 to the condenser 36). The dischargevalve 200 may be a solenoid type valve, or may be a mechanical checkvalve. In the illustrated embodiment, the discharge valve 200 is asolenoid valve, controlled by the control 30. Notably, when thecompressor does not run in the pulse width modulation mode, this valveis normally open, such that refrigerant can flow through the dischargetube 202 and to the condenser 36 relatively unimpeded. A bypass line 204selectively bypasses the refrigerant from the discharge tube 202 (or thedischarge line 206, or the discharge pressure chamber 123) hack to thesuction chamber 121. A bypass valve 216 is positioned on the bypass line204. The bypass valve 216 typically needs to be open within the timeinterval of 0 to 0.2 seconds of (before or after) the closing of thepulse width modulation valve 210.

When the control moves the suction valve 210 to a closed position, thedischarge valve 200 is also closed and the bypass valve 216 is opened.In this manner, the refrigerant is returned from the discharge chamber123 to the suction chamber 121. At the same time, the closed dischargevalve 200 blocks the backflow of refrigerant from the discharge line 206into the discharge chamber 123. Therefore, the pressure in the dischargechamber 123 can now be maintained at the same or nearly the same lowpressure as the pressure in the suction chamber 121. This reduces powerconsumption of the compressor motor 28, because the refrigerant nolonger needs to be compressed to the pressure, corresponding to the highpressure in the condenser 36. The discharge valve 200 typically needs tobe open within the time interval of 0 to 0.2 seconds of (before orafter) the closing of the pulse width modulation valve 210. Thedischarge valve 200, if it is a solenoid type valve, can be typicallyclosed within the range of 0 to 0.2 seconds of the closing of the valve210. If the discharge valve 200 were, for example, a mechanical checkvalve, it would shut close automatically, as the refrigerant from thecondenser 36 would begin to move into chamber 123 closing the dischargevalve 200.

FIG. 2 shows a so-called PV diagram that represents compression processin the compressor 21. In this diagram, P is changing pressure within thescroll elements and V is changing compression volume within the scrollelements for the compressor 21. The area covered by the PV diagram isindicative of the power consumed by the compressor 21. As shown in FIG.2, the cross-hatched area (ABC) is indicative of the power consumed bythe compressor 21 incorporating the invention when the pulse widthmodulation valve 210 is in the closed position and the inventive bypassarrangement is present. The non-cross hatched area (DEFG) is indicativeof the power consumed by the compressor 21 without the inventive bypassline when the pulse width modulation valve 210 is closed. As can beappreciated, the present invention can save substantial amount ofenergy, as shown by comparison of the above two areas in FIG. 2. Itshould be understood that this graph is an illustration, and actualresults will vary for any given compressor and operating conditions. Asalso shown in FIG. 2, the point G indicates pressure within thecompressor suction cavity 121 without the inventive bypass arrangementwhen the suction modulation valve 210 is in the closed position. Asknown, this pressure needs to be maintained above a certain thresholdfor compressors with hermetically sealed motors (if this pressuredecreases below a certain value, the motor terminal pins can be damagedby a so-called “corona discharge” effect, which occurs at near vacuumconditions in the compressor suction cavity 121). Normally, thispressure is kept at about 1 psia level. Without the bypass arrangement,the pressure in the discharge chamber 123 will be at the dischargepressure indicated by point F.

When the bypass arrangement is employed, the pressure will be relievedto the pressure approaching the suction pressure, as indicated by thepoint C. Since in the inventive arrangement, the discharge pressure isreduced from F to C, the motor would consume less power, due to reducedamount of work required to compress the refrigerant. Also, it has to benoted that, for this inventive bypass arrangement, the suction pressurewould increase somewhat from the pressure indicated by the point G tothe pressure indicated by the point C. This occurs as some of therefrigerant trapped on the discharge side is re-expanded back into thesuction chamber 121, causing the pressure in the suction chamber 121 torise above the pressure indicated by the point G, which was the pressurelevel in the prior art pulse width modulation arrangement.

It should be understood that although this invention is described inrelation to refrigerant systems incorporating scroll compressors, it isapplicable to various compressor types, including screw compressors,reciprocating compressors, rotary compressors, etc. It is can also beapplied to different refrigerant systems, including residential airconditioning applications, container and truck-trailer applications,heat pump application, supermarket applications, rooftop applications,etc. The refrigerant systems can also include additional features, suchas economized circuit, employing a compressor having a vapor injectionline. The compressor can also have bypass line, which bypassesrefrigerant from an intermediate compression point to suction. If theintermediate to suction line bypass line is employed, then theconnection between the discharge bypass, described in this application,and compressor suction can also be established via the intermediate tosuction bypass line. Of course this invention would apply to varioustypes of refrigerants, such, for example, R410A, R134a, R22, R407C,R744, etc.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

1. A refrigerant system comprising: a compressor compressing refrigerantto a discharge pressure and an electric motor for driving saidcompressor, said compressor housed within a housing shell; a condenserpositioned downstream of said compressor, an expansion device positioneddownstream of said condenser, and an evaporator positioned downstream ofsaid expansion device; a suction valve positioned on a suction lineleading from said evaporator into said compressor housing shell; acontrol for using pulse width modulation for cycling said suction valvebetween an open position and a closed position, said suction valveblocking the flow of a refrigerant through the suction line when in theclosed position; and a bypass line for selectively bypassing refrigerantcompressed to a discharge pressure by said compressor downstream of saidsuction valve, and said bypass line including a bypass valve, saidbypass valve being controlled by said control, said bypass valve beingopened when said suction valve is closed by said control.
 2. Therefrigerant system as set forth in claim 1, wherein said compressor isselected from the group consisting of a scroll compressor, a rotarycompressor, a reciprocating compressor, and a screw compressor.
 3. Therefrigerant system as set forth in claim 1, wherein a discharge valve isalso positioned on the discharge side of the compressor and downstreamof said bypass line.
 4. The refrigerant system as set forth in claim 3,wherein said discharge valve is closed when said suction valve iscontrolled to be closed and said bypass valve is controlled to beopened.
 5. The refrigerant system as described in claim 4, wherein saiddischarge valve is closed in the time interval between 0 and 0.2 secondsof the closure of said suction valve.
 6. The refrigerant system asdescribed in claim 4, wherein said bypass valve is opened in the timeinterval between 0 and 0.2 seconds of the closure of said suction valve.7. The refrigerant system as set forth in claim 1, wherein said bypassline returns refrigerant to said suction line at a position downstreamof said suction valve.
 8. The refrigerant system as set forth in claim1, wherein said bypass valve is opened in the time interval between 0and 0.2 seconds of the closure of said suction valve.
 9. A method ofoperating a refrigerant system comprising the steps of: (1) providing acompressor for compressing refrigerant to a discharge pressure and anelectric motor for driving said compressor, said compressor housedwithin a housing shell; (2) providing a condenser positioned downstreamof said compressor, an expansion device positioned downstream of saidcondenser, and an evaporator positioned downstream of said expansiondevice; (3) providing a suction valve positioned on a suction lineleading from said evaporator into said compressor housing shell; (4)using pulse width modulation for cycling said suction valve between anopen position and a closed position, said suction valve blocking theflow of a refrigerant through the suction line when in the closedposition; and (5) selectively bypassing refrigerant compressed to adischarge pressure by said compressor downstream of said suction valve,and a bypass line including a bypass valve, said bypass valve beingcontrolled by said control, said bypass valve being opened when saidsuction valve is closed by said control.
 10. The method as set forth inclaim 9, wherein a discharge valve is also positioned on the dischargeside of the compressor and downstream of said bypass line.
 11. Themethod as set forth in claim 9, wherein said discharge valve is closedwhen said suction valve is controlled to be closed and said bypass valveis controlled to be opened.
 12. The method as described in claim 11,wherein said discharge valve is closed in the time interval between 0and 0.2 seconds of the closure of said suction valve.
 13. The method asdescribed in claim 11, wherein said bypass valve is opened in the timeinterval between 0 and 0.2 seconds of the closure of said suction valve.14. The method as set forth in claim 9, wherein said bypass line returnsrefrigerant to said suction line at a position downstream of saidsuction valve.
 15. The method as set forth in claim 9, wherein saidbypass valve is opened in the time interval between 0 and 0.2 seconds ofthe closure of said suction valve.